Network having a resistance the temperature coefficient of which is variable at will

ABSTRACT

A temperature compensation network having a resistance that exhibits a temperature coefficient that is adjustable substantially independently of the voltage applied to the network. The network includes a resistive voltage divider connected in parallel with the emitter-collector path of a transistor. The base of the transistor is connected to a tapping on the voltage divider. A zener diode having a zero temperature coefficient relative to the transistor temperature coefficient is connected to the voltage divider, whereby the network exhibits a net negative temperature coefficient of resistance.

.Ilnited States Patent Wouterus Bom [451 Jan. 25, 1972 [54] NETWORK HAVING A- RESISTANCE .THE TEMPERATURE CQEFFICIENT OF WHICH IS VARIABLE AT WILL [72] Inventor: Johannes Gerardus Wouterus Bom, Em-

masingel. Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New York, NY.

[22] Filed: May 19, 1969 [21] Appl. No.: 825,825

I [30] Foreign Application Priority Data May 17, 1968 Netherlands ..6806969 [52] U.S. Cl ..307/3l0, 307/3 I 8 [51] Int. Cl. ..H03k [58] Field ofSearch ..307/310,318;330/23;33l/66 [56] References Cited UNITED STATES PATENTS 3,214,706 10/1965 Mollinga 307/3l8 X 3,488,529 l/l970 Howe .307/3l0 Primary Examiner-Roy Lake Assistant Examiner-lames B. Mullins Attorney-Frank R. Trifari [57] ABSTRACT A temperature compensation network having a resistance that exhibits a temperature coefticient that is adjustable substantially independently of the voltage applied to the network. The network includes a resistive voltage divider connected in parallel with the emitter-collector path of a transistor. The base of the transistor is connected to a tapping on the voltage divider. A zener diode having a zero temperature coefficient relative to the transistor temperature coefficient is' connected to the voltage divider, whereby the network exhibits a net negative temperature coefficient of resistance.

13 Claims, 5 Drawing Figures mi N H?!) JANQES mm: 3.638.049

+Vs +Vs fag] fl .2

PRIOR ART PRIOR ART INVENTOR.

JOHANNES G.W. BOM

BY (2AM AGEKIT sistance of the transistor NETWORK HAVING A RESISTANCE THE TEMPERATURE COEFFICIENT OF WHICH IS VARIABLE AT WILL The present invention'relates to a network having a resistance with a temperature coefficient that is variable at will. Such networks are often required, especially in semiconductor technology, in order to compensate for the temperature coefficient of an entire circuit arrangement or of an important part thereof.

The British Pat. specification No. 1,093,316 describes a circuit arrangement for compensating the temperature-dependent variations of a current flowing through a temperature-dependent element supplied through the emitter-collector path of a first transistor, the current flowing through the said transistor being controlled by a control magnitude. According to this patent, the control circuit includes, for temperature compensation, the emitter-collector path of a further transistor having a resistive voltage divider connected in parallel therewith and to the tapping of which the base of the further transistor is connected. The resistance value of the part of the voltage divider connected between the emitter and the base of the further transistor is smaller than the value of the base-emitter input impedance of the further transistor, and the current through the whole of the voltage divider is smaller than the collector current of the further transistor. This arrangement thus mainly comprises a network having a resistance with a temperature coefficient that is variable at will and including the parallel connection of a resistive voltage divider and the emitter-collector path of a transistor the base of which is connected to the tapping of the voltage divider.

The temperature coefficient C,,,, of this network is equal to the temperature coefficient C of the internal base-emitter remultiplied by the ratio V,/V,, between the voltage set up across the network (V and the voltage operative between the base and the emitter (V,,,,) of the transistor. Consequently, C is also influenced by the choice of V, and it is not possible to obtain a given desired value of C for each arbitrary value of V For a given value of C,,,, a

variation of V, requires a proportional variation of V Therefore a variation of the value of one of the resistors of the resistive voltage divider requires a variation of the value of the other resistor thereof. As a result, it is difficult to achieve the desired adjustment. In an embodiment of the circuit arrangement described in the above-mentioned patent specification, this difficulty is avoided by feeding the base-emitter circuit of the transistor of the network, more or less independently of V from a separate supply source through a variable resistor connected to a second tapping on the part of the resistive voltage divider which is connected between the base and the emitter of the transistor.

It is an object of the invention to provide an improved network of the kind described, the temperature coefficient of which can be chosen substantially independently of the reverse collector voltage set up across the network, no separate supply source for the base-emitter circuit of the transistor being required.

According to the present invention an element having a temperature coefficient substantially equal to, arid including at least one Zener diode, is connected in the voltage divider so that the temperature coefficient of the network can be chosen substantially independently of the reverse collector voltage set up across the network.

In order that the invention may readily be carried into effect, it will now be described in greater detail, by way of example, with reference to the accompanying drawing, in which:

FIG. 1 is the circuit diagram of the network used in the arrangement described in British Pat. specification No. 1,093,316,

FIG. 2 is the circuit diagram of a modification of this network described in the said patent specification,

FIG. 3 is the circuit diagram of a first embodiment of the network in accordance with the invention,

FIG. 4 is the circuit diagram of a second embodiment thereof, and

FIG. 5 is the circuit diagram of a third simplified embodiment thereof.

FIG. 1 shows the network described in British Pat. specification No. 1,093,3l6 and having a temperature coefficient which is variable at will. This network is constituted by the parallel connection of the resistive voltage divider comprising resistors 2, 3 and 4 and of the emitter-collector path of a transistor 1, for example, an NPN-transistor, the base of which is connected to the junction of the resistors 2 and 3 of the voltage divider. The value of the part 2 of the voltage divider connected between the-emitter. and the base of the transistor 1 is made smaller than that of the base-emitter input impedance of the transistor 1. The overall resistance R,=R +R +R,, of the voltage divider 2, 3, 4 is chosen to be such that the current I, flowing through this voltage divider is smaller than the collector current 1 of the transistor. At a given reverse collector voltage +V, this is accomplished by making the value R of the resistor 2 small as compared with the forward base-emitter resistance R of the transistor 1, and by making the overall resistance value R,=R +R +R of the voltage divider such that The collector current I is equal to (of-l) times the base current 1 which in turn is equal to the quotient V /R (the base-emitter voltage divided by the base-emitter resistance). Since R is made smaller than R V is about equal to V, R /R, but R is dependent on the temperature and also on V and hence on V The collector current I, and consequently the overall resistance R of the network also vary with temperature and under the conditions set forth, the temperature coefficient C, of this variation is equal to V,/V,,,., or approximately R,/R times the temperature coefficient C of the base-emitter resistance of the transistor, provided that the collector-base current gain factor a'1 of the transistor is greater than the feed back factor R lR- which limits the gain.

Varying the voltage V, causes the base-emitter voltage V and hence the base current 1 and the collector current I, to vary, which usually is undesirable. Subsequent readjustment of the collector current 1 to the desired value, for example, by varying the resistor 4, involves a change in the ratio R,/R and hence in the total temperature coefficient C which consequently can be selected only in a given relationship with the voltage V,.

The modification shown in FIG. 2 and described in the above-mentioned patent specification has l of freedom more. In this arrangement the resistive voltage divider is provided with a second tapping between two parts 2 and 2' of its base branch, its collector-base branch comprising only the resistor 3. The second tapping is connected through a further resistor 5 to separate voltage source +Vg of, for example, constant or stabilized forward base voltage.

The resistive voltage divider 2, 2, 3 satisfies the above conditions so that:

The voltage V, of the auxiliary voltage source and the valve of the resistor 5 are chosen so that the forward base-emitter voltage V and the base-current l are mainly determined by these magnitudes and that the resistance value R of the further resistor 5 has substantially no influence on the effective value of the base-emitter branch of the voltage divider 2, 2, 3:

VI V, R. 7?

IOIOZO This circuit arrangement has the disadvantage of requiring a separate voltage source having a substantially constant voltage relative to the emitter of the transistor 1 must be substantially constant. Nevertheless, there is still a slight but inevitable influence ofthe adjustment of I on the value of C,,,,.

In the embodiment of the network in accordance with the invention shown in FIG. 3, the resistive voltage divider comprises a resistor 2 connected between the base and the emitter of a transistor 1 and a resistor 3 with the end remote from the base connected to the tapping on a further resistive voltage divider 9, 9'. The latter voltage divider is connected in parallel with a Zener diode 7, this parallel connection being connected at one end to the voltage source +V, and at the other end through a resistor 8 to the emitter of the transistor 1. This network also satisfies the above conditions:

R R,,,, and l the current through the voltage dividers I +I where and I R. R2 R. Furthermore,

must be small as compared with R Under these conditions the temperature coefficient of the network is tt x 2 Ir 9 9" 7i where C, is the temperature coefficient of the Zener diode 7. This Zener diode may be selected to have a very small temperature coefficient, for example, a coefficient which compared with that of the transistor, C is substantially equal to zero. The Zener voltage V, across the diode 7 must be at least equal to the desired range V,,,, ,-V of the voltage across the network. If for the desired value of V no Zener diode 7 having a temperature coefficient of substantially zero can be found, this diode may be replaced by the series connection of one or several Zener diodes 7, 7' and one or several diodes l0, 10' connected in the forward direction, the Zener diodes and the other diodes being chosen so that the desired overall voltage drop V,=V,+V '+V, +V is obtained and the temperature coefficient C, of the Zener diode is compensated for by that of the other diodes:

Under these conditions, the overall temperature coefiicient C,,,, of the network may be freely chosen by means of the ratio R /R and of the temperature coefficient C of the transistor 1, while independently thereof the collector current I, and consequently the voltage V, across the network may be varied within given limits by varying the voltage across the voltage divider 2, 3.

The collector circuit of the transistor 1 further includes a protective resistor 6 for limiting I to a permissible value, for example, in the case of an excessive voltage across the voltage divider 2, 3:

In an arrangement including temperature-sensitive elements which is to be controlled in accordance with the value of the voltage V,, the described network may be used as a temperature-dependent compensating resistor having a temperature coefficient which is adjustable or variable at will. Alternatively, the network may be used as a first stage of the arrangement which compensates for the influence of the temperature. the control voltage for the next stage being derived either between the emitter and the collector of the transistor 1 or, with inversion of the temperature influence, across the resistor 6.

FIG. 4 is the circuit diagram ofa second embodiment of the network in accordance with the invention.

In this embodiment the Zener diode 7 is connected in series with two diodes 10 connected in the forward direction so that its temperature coefficient is compensated. The series connection of the diodes 7 and 10, shunted by the voltage divider 9, 9', is included in the first voltage divider between the resistors 2 and 3. Since the temperature coefficient of the section 7, I0 is substantially equal to zero, the overall temperature coefficient C again is equal to and hence can be chosen by means of the resistors 2 and 3, while independently thereof the working point of the transistor 1 can be determined by means of the second voltage divider 9,9.

In many applications it is not necessary for I and hence for V, to be variable, but the desired invariable value of J is smaller than corresponds with the ratio R /R determined by C In such cases the simplified modification shown in FIG. 5 may be used: C may be freely chosen by means of the temperature coefficient C,, of the transistor and of the ratio R /R while independently thereof V, and hence I, can be freely chosen by means of V =V +V +V +V ol The networks in accordance with the present invention are especially intended for use in series with other elements, such as resistors, so as to compensate for the temperature coefficient or coefficients either of one or more further elements of a circuit or arrangement, or of an entire circuit or arrangement, for example, as described in the above-mentioned British Pat. specification No. 1,093,316. At the same time they may serve as input stages of such circuits or arrangements.

Iclaim:

1. A temperature dependent network having a resistance with a temperature coefficient that is variable at will comprising, a transistor, a plurality of resistance elements connected to form a resistive voltage divider, means connecting the resistive voltage divider in parallel with the emitter-collector path of the transistor, means connecting the base of the transistor to a tapping on the voltage divider so that the resistance value of the part of the voltage divider connected between the emitter and the base of the transistor is smaller than the value of the base-emitter input impedance of the transistor, the overall resistance value of the voltage divider being chosen so that the current through the whole of the voltage divider is smaller than the collector current of the transistor, an element having a temperature coefficient that is substantially equal to zero relative to the transistor temperature coefficient and including at least one Zener diode, and means connecting said element in the voltage divider so that the temperature coefficient of the network can be chosen substantially independently of the reverse collector voltage set up across the network.

2. A network as claimed in claim 1, characterized in that the element includes at least one diode connected in series with the Zener diode in the forward direction so as to substantially compensate for the temperature coefficient of the Zener diode.

101020 OIA' 3. A network as claimed in claim 1, characterized in that the element including the Zener diode is connected to the emitter of the transistor through a resistor.

4. A network as claimed in claim 4, characterized in that the collector circuit of the transistor includes a further resistor.

5. A network as claimed in claim 1 wherein the last-named connecting means is arranged to connect a part of the resistive voltage dividerin parallel with said zero temperature coefficient element, and means connecting a tapping on said parallel part of the voltage divider to the base of the transistor.

6. A temperature-sensitive network with a temperature coefficient of resistance that is adjustable substantially independently of the voltage appliedto the network comprising, a pair of input terminals, a transistor with a given temperature coefficient, a constant voltage element with a temperature coefficient that is negligible relative to said given temperature coefficient of the transistor, a resistive voltage divider, means connecting the constant voltage element in series with the voltage divider across the network input terminals, and means connecting the emitter-collector path of the transistor in parallel with the resistive voltage divider and the base electrode to a tapping on the voltage divider such thatthe resistance of the part of the voltage divider between the base and emitter of the transistor is smaller than the transistor baseemitter input impedance.

7. A network as claimed in claim 6 wherein said constant voltage element comprises a Zener diode in series with a diode of approximately equal and opposite temperature coefficient.

8. A network as claimed in claim 7 wherein said Zener diode and diode are connected in series in that part of the voltage divider connected between the base and collector of the transistor.

9. A network as claimed in claim 6 wherein said constant voltage element comprises a Zener diode, said network further comprising a second resistive voltage divider connected in parallel with the Zener diode, and wherein the base electrode of the transistor is directly connected to a tapping 5 on the second voltage divider.

10. A network as claimed in claim 9 wherein the first voltage divider comprises first and second resistors, and wherein said first resistor, said Zener diode and said second resistor are serially connected in the order named across the network input terminals.

11. A network as claimed in claim 6 further comprising a second resistive voltage divider connected in parallel with said constant voltage element, and means connecting a tapping on said second voltage divider to the base of the transistor.

12. A network as claimed in claim 13 wherein said constant voltage element comprises a Zener diode.

13. A temperature sensitive network with a temperature coefficient of resistance that is adjustable substantially independently of the voltage applied to the network comprising, a pair of input terminals, a transistor with a given temperature coefficient, a zener diode with a temperature coefficient that is negligible relative to the transistor temperature coefficient, a first resistive voltage divider, a second resistive voltage divider connected in parallel with the zener diode and across the input terminals, means connecting the first voltage divider to a tapping on the second voltage divider, and means including a part of said second voltage divider for connecting the emittercollector path of the transistor in parallel with the first resistive voltage divider and the base electrode to a tapping thereon such that the resistance'of the part of the first voltage divider between the base and emitter of the transistor is smaller than the transistor base-emitter inputfimpedance. 

1. A temperature dependent network having a resistance with a temperature coefficient that is variable at will comprising, a transistor, a plurality of resistance elements connected to form a resistive voltage divider, means connecting the resistive voltage divider in parallel with the emitter-collector path of the transistor, means connecting the base of the transistor to a tapping on the voltage divider so that the resistance value of the part of the voltage divider connected between the emitter and the base of the transistor is smaller than the value of the baseemitter input impedance of the transistor, the overall resistance value of the voltage divider being chosen so that the current through the whole of the voltage divider is smaller than the collector current of the transistor, an element having a temperature coefficient that is substantially equal to zero relative to the transistor temperature coefficient and including at least one Zener diode, and means connecting said element in the voltage divider so that the temperature coefficient of the network can be chosen substantially independently of the reverse collector voltage set up across the network.
 2. A network as claimed in claim 1, characterized in that the element includes at least one diode connected in series with the Zener diode in the forward direction so as to substantially compensate for the temperature coefficient of the Zener diode.
 3. A network as claimed in claim 1, characterized in that the element including the Zener diode is connected to the emitter of the transistor through a resistor.
 4. A network as claimed in claim 4, characterized in that the collector circuit of the transistor includes a further resistor.
 5. A network as claimed in claim 1 wherein the last-named connecting means is arranged to connect a part of the resistive voltage divider in parallel with said zero temperature coefficient element, and means connecting a tapping on said parallel part of the voltage divider to the base of the transistor.
 6. A temperature-sensitive network with a temperature coefficient of resistance that is adjustable substantially independently of the voltage applied to the network comprising, a pair of input terminals, a transistor with a given temperature coefficient, a constant voltage element with a temperature coefficient that is negligible relative to said given temperature coefficient of the transistor, a resistive voltage divider, means connecting the constant voltage element in series with the voltage divider across the network input terminals, and means connecting the emitter-collector path of the transistor in parallel with the resistive voltage divider and the base electrode to a tapping on the voltage divider such that the resistance of the part of the voltage divider between the base and emitter of the transistor is smaller than the transistor base-emitter input impedance.
 7. A network as claimed in claim 6 wherein said constant voltage element comprises a Zener diode in series with a diode of approximately equal and opposite temperature coefficient.
 8. A network as claimed in claim 7 wherein said Zener diode and diode are connected in series in that part of the voltage divider connected between the base and collector of the transistor.
 9. A network as claimed in claim 6 wherein said constant voltage element comprises a Zener diode, said network further comprising a second resistive voltage divider connected in parallel with the Zener diode, and wherein the base electrode of the transistor is directly connected to a tapping on the second voltage divider.
 10. A network as claimed in claim 9 wherein the first voltage divider comprises first and second resistors, and wherein said first resistor, said Zener diode and said second resistor are serially connected in the order named across the network input terminals.
 11. A network as claimed in claim 6 Further comprising a second resistive voltage divider connected in parallel with said constant voltage element, and means connecting a tapping on said second voltage divider to the base of the transistor.
 12. A network as claimed in claim 13 wherein said constant voltage element comprises a Zener diode.
 13. A temperature sensitive network with a temperature coefficient of resistance that is adjustable substantially independently of the voltage applied to the network comprising, a pair of input terminals, a transistor with a given temperature coefficient, a zener diode with a temperature coefficient that is negligible relative to the transistor temperature coefficient, a first resistive voltage divider, a second resistive voltage divider connected in parallel with the zener diode and across the input terminals, means connecting the first voltage divider to a tapping on the second voltage divider, and means including a part of said second voltage divider for connecting the emitter-collector path of the transistor in parallel with the first resistive voltage divider and the base electrode to a tapping thereon such that the resistance of the part of the first voltage divider between the base and emitter of the transistor is smaller than the transistor base-emitter input impedance. 